From 8656a0e819cf6a54ac6f8a8f4b6e6c2a29bd5ea5 Mon Sep 17 00:00:00 2001
From: Kevin Dunlap <kjd@ucbvax.Berkeley.EDU>
Date: Fri, 23 May 1986 16:36:28 -0800
Subject: [PATCH] document distributed with 4.1BSD

SCCS-vsn: old/roff/USD.doc/troff.tutorial/tt08 4.1
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+.\"	@(#)tt08	4.1 (Berkeley) %G%
+.\"
+.NH
+Introduction to Macros
+.PP
+Before we can go much further in
+.UL troff ,
+we need to learn a bit about the
+macro
+facility.
+In its simplest form, a macro is just a shorthand notation
+quite similar to a string.
+Suppose we want every paragraph to start
+in exactly the same way _
+with a space and a temporary indent of two ems:
+.P1
+^sp
+^ti +2m
+.P2
+Then to save typing, we would like to collapse these into
+one shorthand line,
+a
+.UL troff
+`command' like
+.P1
+^PP
+.P2
+that would be treated by
+.UL troff
+exactly as
+.P1
+^sp
+^ti +2m
+.P2
+.BD .PP
+is called a
+.ul
+macro.
+The way we tell
+.UL troff
+what
+.BD .PP
+means is to
+.ul
+define
+it with the
+.BD .de
+command:
+.P1
+^de PP
+^sp
+^ti +2m
+^^
+.P2
+The first line names the macro
+(we used
+.BD .PP ' `
+for `paragraph',
+and upper case so it wouldn't conflict with
+any name that
+.UL troff
+might
+already know about).
+The last line
+.BD ..
+marks the end of the definition.
+In between is the text,
+which is simply inserted whenever
+.UL troff
+sees the `command'
+or macro call
+.P1
+^PP
+.P2
+A macro
+can contain any mixture of text and formatting commands.
+.PP
+The definition of
+.BD .PP
+has to precede its first use;
+undefined macros are simply ignored.
+Names are restricted to one or two characters.
+.PP
+Using macros for commonly occurring sequences of commands
+is critically important.
+Not only does it save typing,
+but it makes later changes much easier.
+Suppose we decide that the paragraph indent is too small,
+the vertical space is much too big,
+and roman font should be forced.
+Instead of changing the whole document,
+we need only change the definition of
+.BD .PP
+to
+something like
+.P1
+^de PP	\e" paragraph macro
+^sp 2p
+^ti +3m
+^ft R
+^^
+.P2
+and the change takes
+effect everywhere we used
+.BD .PP .
+.PP
+.BD \e"
+is a
+.UL troff
+command that causes the rest of the line to be ignored.
+We use it here to add comments to the macro
+definition
+(a wise idea once definitions get complicated).
+.PP
+As another example of macros,
+consider these two which start and end a block of offset,
+unfilled text, like most of the examples in this paper:
+.P1
+^de BS	\e" start indented block
+^sp
+^nf
+^in +0.3i
+^^
+^de BE	\e" end indented block
+^sp
+^fi
+^in \(mi0.3i
+^^
+.P2
+Now we can surround text like
+.P1
+Copy to
+John Doe
+Richard Roberts
+Stanley Smith
+.P2
+by the commands
+.BD .BS
+and
+.BD .BE ,
+and it will come out as it did above.
+Notice that we indented by
+.BD .in\ +0.3i
+instead of
+.BD .in\ 0.3i .
+This way we can nest our uses of
+.BD .BS
+and
+.BD BE
+to get blocks within blocks.
+.PP
+If later on we decide that the indent
+should be 0.5i, then it is only necessary to
+change the definitions of
+.BD .BS
+and
+.BD .BE ,
+not the whole paper.
-- 
2.20.1